Ukraine crisis: Slavyansk pro-Russian rebels shoot down two helicopters as 'Kiev forces launch military operation'

Ukrainian government forces have launched an anti-terror operation to retake the rebel stronghold of Slavyansk, with two troops reported dead and others wounded after separatists used grenade launchers to down military helicopters surrounding the city.

Pro-Russian rebels shot down two Ukrainian helicopters, killing two crew, after Ukrainian officials said Slavyansk was "tightly surrounded" and called on separatist leaders to release hostages and surrender.

Russia had vowed "catastrophic consequences" if Kiev conducted a military operation on Thursday, The Voice of Russia has reported.

A third helicopter, believed to be carrying medical staff was hit and one of the crew was wounded as a result, according to Sky News.

Interior Minister Arsen Avakov said the offensive was answered with heavy artillery, with the rebels using grenade and portable anti-aircraft missile launchers to bring down planes.

"As a result of the shooting, two troops from the Ukrainian army were killed," Ukraine's Interior Ministry said in a statement.

Today, Russian President Vladimir Putin's spokesperson accused Kiev of launching a "punitive operation" in south-east Ukraine, destroying the final hope of keeping alive the Geneva agreement designed to defuse the crisis, Russian news agencies reported.

The European Union said it is watching events "with increasing concern".

Vyacheslav Ponomarev, the insurgency-appointed mayor of Slavyansk, said self-defence forces had shot down two helicopters, killing one pilot and capturing the other. Details of these claims could not be independently verified.

Describing the operation as "the active phase of the anti-terrorist operation", Mr Avakov said its goals were simple - "free the hostages, lay down their arms and free administrative buildings, and restore the normal functioning of the town's administration".

On the road leading into Slavyansk from Kramatorsk to the south, trucks were parked sideways to block the road.

The fighting began at 4am (1am GMT), officials and local residents said. Ukrainian troops could be in seen in armoured personnel carriers in a southern suburb of Slavyansk.

An Associated Press cameraman reported seeing black plumes of smoke on the edge of the city. An emergency siren had sounded at dawn.

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If the Ukrainian military action is confirmed, it would be the first major assault against the insurgents, who have seized police stations and other government buildings in about a dozen cities in southeastern Ukraine.

The violence comes after Mr Putin said yesterday that Ukraine should withdraw its military from the eastern and southern regions of the country.

Just hours later Ukraine’s interim president announced the renewal of military conscription for men aged between 18 and 25 after admitting earlier this week police and security forces had been effectively "helpless" to quell the unrest in the Donetsk and Luhansk regions.

Oleksandr Turchynov said efforts would instead be focused on preventing the instability from spreading to other parts of the country.